Submitted to DHC Working Group Yves T'Joens
INTERNET DRAFT Christian Hublet
<draft-ietf-dhc-pv4-reconfigure-05.txt> Alcatel
Peter De Schrijver
Mind
June 2001
Expires November, 2001
DHCP reconfigure extension
Status of this memo
This document is an Internet-Draft and is in full conformance with
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Abstract
This draft defines extensions to DHCP [DHCP] to allow dynamic
reconfiguration of a single host triggered by the DHCP server (eg. a
new IP address and/or local configuration parameters). This is
achieved by introducing a unicast FORCERENEW message which forces the
client to the RENEW state. The behaviour for hosts using the DHCP
INFORM message to obtain configuration information is also described.
1. Introduction
The procedures as described within this draft allow the dynamic
reconfiguration of individual hosts.
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1.1 Conventions
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY" and "OPTIONAL" in this
document are to be interpreted as described in RFC 2119 [RFC2119].
2. DHCP force renew
This section describes the FORCERENEW message extension.
2.1 Terminology
DHCP client : host to be reconfigured using DHCP.
DHCP server : server which configured the DHCP client.
2.2 Force renew procedures
The DHCP server sends a unicast FORCERENEW message to the client.
Upon receipt of the unicast FORCERENEW message, the client will
change its state to the RENEW state, and will then try to renew its
lease according to normal DHCP procedures. If the server wants to
assign a new IP address to the client, it will reply to the DHCP
REQUEST with a DHCP NAK. The client will then go back to the init
state and broadcast a DHCP DISCOVER message. The server can now
assign a new IP address to the client by replying with a DHCP OFFER.
If the FORCERENEW message is lost, the DHCP server will not receive a
DHCP REQUEST from the client and it should retransmit the FORCERENEW
message using an exponential backoff algorithm. Depending on the
bandwidth of the network between server and client, the server should
choose a delay. This delay grows exponentially as retransmissions
fail. The amount of retransmissions should be limited.
The procedures described above assume the server to send a unicast
FORCERENEW message to the client. Receipt of a multicast FORCERENEW
message by the client should be silently discarded.
It can be that a client has obtained a network address through some
other means (e.g., manual configuration) and has used a DHCP INFORM
request to obtain other local configuration parameters. Such clients
should respond to the receipt of a unicast FORCERENEW message with a
new DHCP INFORM request so as to obtain a potential new set of local
configuration parameters. Note that the usage of these procedures are
limited to the set of options that are eligible for configuration by
DHCP and should not override manually configured parameters.
Note further that usage of the FORCERENEW message to reconfigure a
client address or local configuration parameters can lead to the
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interruption of active sessions, and that as such these procedures
should be used in controlled circumstances.
2.3 Example usage
2.3.1 Embedded DHCP clients
The autoconfiguration of home gateways (more generically Network
Termination equipment) for public networking purposes can be achieved
through means of DHCP, as described in [DSL_autoconf]. In order to
allow service changes or service interruption, the FORCERENEW message
can trigger the home gateway to contact the DHCP server, prior to the
expiry of the lease.
2.3.2 Hospitality service scenario
In self provisioned networks, e.g., hotel rooms, the hotel owned DHCP
server can hand out limited use IP addresses, that allows the
customer to consume local services or select external services from a
web browser interface. In order to allow external services through
other service providers, e.g., global internet services or enterprise
VPN services, the DHCP server can trigger the client to ask for a new
DHCP initialization session so as to obtain e.g., a globally routed
IP address.
2.3.3 Network renumbering
Under tightly controlled conditions, the FORCERENEW procedures can be
used to brute force the renumbering of entire subnets, client per
client, under control of a DHCP server.
2.4 Rationale
The approach as described in this document has a number of
advantages. It does not require new states to be added to the DHCP
client implementation. This minimizes the amount of code to be
changed. It also allows lease RENEWAL to be driven by the server,
which can be used to optimize network usage or DHCP server load.
3. Extended DHCP state diagram
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+--------+ +------+
| Init / | +-->+ Init +<---------------+-------------------+
| Reboot | | +--+---+ | |
+---+----+ DHCPNAK/ -/Send DHCPDISCOVER | |
| Restart | (broadcast) | |
| | v v-------------+ | |
-/Send DHCPREQUEST| +----+------+ DHCPOFFER/DHCPDECLINE |
| (broadcast)| | Selecting |----------+ | |
v | +----+------+ | |
+---+----+ | DHCPOFFER/DHCPREQUEST | |
| Reboot +---------+ (broadcast) | |
+---+----+ v | |
| +----+-------+ DHCPNAK /halt network
| + Requesting | | lease expired
DHCPACK/ +----+-------+ | |
Record lease | | |
set timers DHCPACK/Record lease | |
| v Set T1 & T2 | |
| +--+----+DHCPFORCE +---+---+ +----+---+
+----------------->+ Bound +---------->+ Renew +--------->+ Rebind |
+--+-+--+T1 expires +-+-+---+T2 expires+----+---+
^ /DHCPREQUEST | | /broadcast |
DHCPACK to leasing | | DHCPREQUEST |
| server | | |
+----------------------------------------+
4. Message layout
The FORCERENEW message makes use of the normal DHCP message layout
with the introduction of a new DHCP message type. DHCP option 53
(DHCP message type) is extended with a new value : DHCPFORCERENEW
(TBD)
5. IANA Considerations
The new value for DHCP option 53 (DHCP message type) to indicate a
DHCPFORCERENEW message is TBD.
6. Security Considerations
As in some network environments FORCERENEW can be used to snoop and
spoof traffic, the FORCERENEW message MUST be authenticated using the
procedures as described in [DHCP-AUTH]. FORCERENEW messages failing
the authentication should be silently discarded by the client.
7. References
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[DHCP] R.Droms, "Dynamic Host Configuration Protocol", RFC 2131,
March 1997.
[DHCP-AUTH] R. Droms et al., "Authentication for DHCP Messages",
RFCxxxx, yyyy 2001.
[DSL_autoconf] Working Text WT-059, "Auto-configuration for Basic
Internet (IP-Based) Services", DSL Forum, May 2001
[RFC2119] S. Bradner, "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997.
8. Acknowledgements
The authors would like to thank David Allan, Nortel, for the
constructive comments to these procedures.
9. Contacts
Yves T'joens
Alcatel Network Strategy Group
Francis Wellesplein 1, 2018 Antwerp, Belgium
Phone : +32 3 240 7890
E-mail : yves.tjoens@alcatel.be
Peter De Schrijver
Mind NV
Vaartkom 11
3000 Leuven
E-mail : p2@mind.be
Christian Hublet
Alcatel Carrier Internetworking Division
De Villermontstraat 28, 2550 Kontich, Belgium
Phone : +32 3 450 3322
E-mail : Christian.Hublet@alcatel.be
8. Full Copyright Statement
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developing Internet standards in which case the procedures for
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